A currently accepted technique for assessing the severity of a stenosis in a blood vessel, including ischemia causing lesions, is fractional flow reserve (FFR). FFR is a calculation of the ratio of a distal pressure measurement (taken on the distal side of the stenosis) relative to a proximal pressure measurement (taken on the proximal side of the stenosis). FFR provides an index of stenosis severity that allows determination as to whether the blockage limits blood flow within the vessel to an extent that treatment is required. The normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and require treatment. Common treatment options include angioplasty and stenting.
Coronary blood flow is unique in that it is affected not only by fluctuations in the pressure arising proximally (as in the aorta) but is also simultaneously affected by fluctuations arising distally in the microcirculation. Minimally invasive sensors may be positioned distally and proximally of the lesion of interest to detect pressures which may then be used to estimate FFR. In traditional pressure sensing FFR procedures, pharmacological hyperemic agents, such as adenosine, are administered to reduce and stabilize the resistance within the coronary arteries. These potent vasodilator agents reduce the dramatic fluctuation in resistance (predominantly by reducing the microcirculation resistance associated with the systolic portion of the heart cycle) to obtain a relatively stable and minimal resistance value.
However, the administration of hyperemic agents is not always possible or advisable. First, the clinical effort of administering hyperemic agents can be significant. In some countries (particularly the United States), hyperemic agents such as adenosine are expensive, and time consuming to obtain when delivered intravenously (IV). In that regard, IV-delivered adenosine is generally mixed on a case-by-case basis in the hospital pharmacy. It can take a significant amount of time and effort to get the adenosine prepared and delivered to the operating area. These logistic hurdles can impact a physician's decision to use FFR. Second, some patients have contraindications to the use of hyperemic agents such as asthma, severe COPD, hypotension, bradycardia, low cardiac ejection fraction, recent myocardial infarction, and/or other factors that prevent the administration of hyperemic agents. Third, many patients find the administration of hyperemic agents to be uncomfortable, which is only compounded by the fact that the hyperemic agent may need to be applied multiple times during the course of a procedure to obtain FFR measurements. Fourth, the administration of a hyperemic agent may also require central venous access (e.g., a central venous sheath) that might otherwise be avoided. Finally, not all patients respond as expected to hyperemic agents and, in some instances, it is difficult to identify these patients before administration of the hyperemic agent.
This application incorporates the following patents and applications by reference herein: U.S. Pat. Nos. 7,930,014 and 8,157,742 along with application Ser. No. 13/460,296 filed: Apr. 30, 2012, entitled: “Devices, Systems, and Methods for Assessing a Vessel;” and application Ser. No. 11/473,974 filed Jun. 23, 2006, entitled “Three Dimensional Co-Registration for Intravascular Diagnosis and Therapy;” and U.S. Provisional Patent Application No. 61/525,736 filed on Aug. 20, 2011 and U.S. Provisional Patent Application No. 61/525,739 filed on Aug. 20, 2011, each of which is hereby incorporated by reference in its entirety.
As described more fully in application Ser. No. 13/460,296 filed: Apr. 30, 2012, entitled: “Entitled: Devices, Systems, and Methods for Assessing a Vessel”, incorporated by referenced herein in its entirety, new techniques have been developed to determine FFR without the use of hyperemic agents.
As recognized in U.S. Pat. No. 8,157,742 entitled “Method and System for Patient-Specific Modeling of Blood Flow,” incorporated by reference herein in its entirety, coronary computed tomographic angiography (CCTA) may be used for imaging of patient with chest pain and involves using computed tomography (CT) technology to image the heart and the coronary arteries following an intra-venous infusion of contrast agent. The CT data is used to generate a 3D model of the heart and coronary arteries. This model is then used to estimate FFR.
CT scanning is a costly procedure and takes time during the critical time a patient is experiencing chest pains. Moreover, the CT machine is not located in the catheter lab where treatment can be administered.
Accordingly, there remains a need for improved devices, systems, and methods for assessing the severity of a blockage in a vessel and, in particular, a stenosis in a blood vessel. In that regard, there remains a need for improved devices, systems, and methods for assessing the severity of a stenosis in the coronary arteries in a staged manner that can quickly assess severity and incorporate additional assessment modalities if more detailed information is needed to assess the patient's condition.